Pulsed laser deposition for growth of high quality epitaxial garnet films for low threshold waveguide lasers

Pulsed laser deposition (PLD) is a mature technique capable of producing extremely high quality epitaxial single crystalline films. We have grown Nd:doped garnet films of GGG (Gd The talk will summarise our progress using conventional (single beam) PLD in thin-film and waveguide growth, using both nanosecond and femtosecond lasers, and also introduce our new directions in tri-beam PLD (three targets, three lasers) for growth of some interesting, complex and perhaps impossible structures, such as Gaussian doping, internal voids and even helically doped structures

High efficiency dye-sensitized solar cells exploiting sponge-like ZnO nanostructures

DSCs based on sponge-like ZnO photoanodes showing conversion efficiency of 6.67% and superior transport properties compared with standard TiO2 nanoparticle

Stress engineering and optimization of thick garnet crystal films grown by pulsed laser deposition

We present here results indicating that stress in films grown by pulsed laser deposition (PLD) may be engineered simply by altering the growth parameters of substrate temperature and laser fluence to balance tensile and compressive stresses. Compositional and structural analysis of Gd3Ga5O12 (GGG) films grown on Y3Al5O12 (YAG) substrates, using three different PLD setups and two different ablating lasers, reveal the effects of different growth parameters on residual stress. Some stress reduction strategies were investigated, including slower heating and cooling ramp rates, and amorphous buffer layers, but changing the growth parameters of substrate temperature and laser fluence was found to have a more significant effect. To characterize the evolution of film stress as thickness increases for different laser fluences, three films were grown in stages to allow substrate curvature measurements and X-ray diffraction analysis to be performed every time the thickness had doubled (from 1-16 µm in thickness). The results from these experiments reveal a compressive stress that relaxes with thickness, thought to be due to lattice mismatch, and leads to the conclusion that stress in PLD grown films of GGG on YAG is a balance between lattice mismatch, thermal expansion mismatch and ion-bombardment

Wettability Control on ZnO Nanowires Driven by Seed Layer Properties

This study proposes a way to control the wettability of zinc oxide nanowires (NWs) by properly selecting the kind of seed layer used to promote the growth of the wires. ZnO seed layers were synthesized on silicon and conductive substrates by a physical vapor deposition approach and a wet-chemical route, namely, the radio frequency magnetron sputtering and the spin-coating techniques, respectively. ZnO NWs were grown by a hydrothermal method on each kind of seed layer and the results were compared. The morphologies and crystallographic orientations of the seed layers and the resulting NWs were investigated with the aim of correlating the characteristics of the underlying seed layer to those of the resulting NWs. Additional insights were obtained by performing optical contact angle (OCA) measurements on ZnO seed layers to study their wettability behavior immediately after the synthesis processes and two weeks later. Hydrophilic behavior was observed in both sputtered and spin-coated fresh seed layers. After two weeks of aging, a change in the wettability and a net transition from hydrophilic to hydrophobic behavior was observed in sputtered seed layers, whereas in the spin-coated films this transition was not so pronounced and was found to be dependent on the precursor concentration. OCA measurements carried out on ZnO NWs showed that the wettability of the NWs is strictly related to the nature of the underlying seed layers and does not depend on the aging time, in contrast to the behavior of the seed layers. Depending on the deposition method, we therefore obtained either highly hydrophilic or superhydrophobic nanowires, which demonstrates the possibility to strongly control the final wetting behavior of these nanostructures for the desired application, such as self-cleaning surfaces, antireflection coatings, or substrates to anchor biofunctional agent

Metal-dielectric nanostructures for amplified Raman and fluorescence spectroscopy

Metal-dielectric nanostructures are synthesized optimizing their capabilities of enhancing Raman scattering and fluorescence emission. Silver nanoparticles with controlled average size and morphology are obtained by dipping porous silicon (p-Si) specimens in silver nitrate acqueous solutions. The effects of silvered p-Si in enhancing Raman Scattering were investigated usinga cyanine dye showing detectable concentration as low as 10-8M. In order to obtain photoluminescence enhancement, silvered p-Si samples are coated by ultrathin films of amorphous silicon nitride. The analysis of metal-dielectric nanostructures show an energy red-shift of the Surface Plasmon resonances connected to the changes of the dielectrics surrounding the metal particles. In particular, the thickness of such a coating can be tuned in order to enhance the fluorescence emission